Sound, such as the human voice or a snapped twig, is produced by releasing mechanical energy from one localized spot into the surrounding medium, such as air. This released energy creates a pressure change around its source, forcing air into mechanical motion. Eventually, these mechanically induced sound waves expand and propagate through the air to the listener.
Over centuries, instrument designers have discovered that terminating the end of an instrument (e.g., a trombone or bugle) with a flared cone increases the instrument's loudness and enhances the purity of the instrument's tone. Similar cones are essential parts of mechanical record players, such as the phonograph 101 of FIG. 1A. A cone shaped component may also act as a mechanical sound amplifier for electromagnetic stadium speakers, such as the exemplary speaker 102 of FIG. 1A (shown in a side and perspective view). A person may even improvise a crude “megaphone” by cupping both hands around their lips to “throw” or project their voice a longer distance.
Acoustic cones have three main functions. First, by gradually expanding the localized source of acoustic energy, a more gentle transition prevents sound from reflecting backwards from the abrupt interface between the source and the air. The cone is the acoustic equivalent of electrical impedance matching, and can increase sound output by a factor of ten or more. Second, in some cases, reflected sound waves re-enter the sound generator, causing the generator to produce distorted or corrupted signals. The fewer back reflections, the purer the sound. Third, the cone may collimate sound into the forward direction, increasing the forward volume levels and allowing the sound to be aimed at listeners in the distance.
In a conventional acoustic cone, such as the “morning glory” shaped cone 101 attached to the needle assembly of a mechanical record player shown in FIG. 1A, there is a single cavity from the narrow to wide end. The cone diameter smoothly increases as the distance from the sound source increases. As illustrated schematically by the density of dots in 150 of FIG. 1B representing a gradient of the intensity of the sound pressure, the sound pressure in a cone decreases away from the smaller end 151 near the source, while simultaneously broadening in area.
Often, the relationship follows a logarithmic curve. This curve is known to optimally reduce reflections back into the record needle assembly, while not over-emphasizing any one frequency. This latter characteristic in critical for an acoustic cone intended to amplify a wide frequency range acoustic source, such a music. A cone with a uniform diameter (e.g., an organ pipe) resonates and tends to favor a single note.
However, such cones are not ideal solutions since they are large and often heavy. In addition, conventional cones tend to be directional, so listeners not facing the lip of the cone hear quieter and somewhat distorted sound images. Also, traditional cones are not easily adjusted to adapt their acoustic properties to match or compensate for deficiencies in the sound source. Furthermore, conventional cones are visually intrusive, such that the cone in current speakers is typically hidden inside a console (e.g., a plastic or wooden console) or a speaker enclosure (e.g., a rectangular speaker enclosure).
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings. The drawings constitute a part of this specification and include exemplary implementations of the present invention and illustrate various objects and features thereof.